The decision comes less than a week after the Mountain West announced that it would postpone all fall sports and explore the possibility of playing football in the spring.
The 6-foot-6 Jackson was voted the 2020 preseason Mountain West Offensive Player of the Year. Last season he led the team with 77 catches for 1,119 yards and eight touchdowns.
"To my family, my teammates, coaches, staff, and the fans, thank you for the love and passion you have shown me during my time wearing the green and gold," Jackson said in a statement. "It has been an honor to play alongside you, play for you, and represent our university over the years. I have grown so much as a man and as a football player during my time in Fort Collins, and for that, I will be forever grateful."
Said coach Steve Addazio: "From day one, Warren Jackson has been all about this football team and developing his game for the next level. He has been the type of leader you want to see from your most talented players. With the postponement of the season, Warren expressed a desire to begin training for his NFL future, and we fully support him in that decision."